Radio tube oscillator



Dec. 13, 1938.

J. MARKOWITZ RADIO TUBE OSCILLATOR Filed Oct. 2'7, 1937 N VENTOR.

ATTORNEY.

Patented Dec. 13, 1938 UNITED STATES PATENT OFFICE 6 Claims.

This invention relates to radio-type audio frequency oscillator devices.

One object of the invention is to furnish an oscillator device of the nature set forth having improved means for producing a current of relatively constant frequency.

Another object of the invention is the provision of a radio-type oscillator having improved char acteristics such that it can be used with a high 10 degree of reliability to provide a sine wave at relatively constant frequency, without requiring complicated or expensive means.

Other objects and advantages of the invention will become apparent as the specification proneeds. a

With the aforesaid objects in view, the inven-- tion consists in the novel combinations and arrangements of parts hereinafter described in their preferred embodiments, pointed out in the subjoined claims, and illustrated in the annexed drawing.

The drawing is a diagrammatic view showing a device embodying the invention.

It will be obvious to those skilled in the art to which the invention appertains. that the same may be incorporated in several diiferent constructions. The accompanying drawing, therefore, is submitted merely as showing the preferred exemplification of the invention.

Generally described, this invention provides a space discharge tube having an inductance coil between the anode and grid, with the cathode connected to an intermediate point of the inductance coil, and a condenser being in parallel with the latter, the capacity whereof is just short of preventing oscillation, whereby a system of unusually high stability is afforded adapted for operation at different frequencies, especially at audio frequency. Further the invention provides a radio type oscillator tube operating preferably at audio frequency and having a. low impedance in the grid circuit, with the latter characterized in that itconstitutes part of the output circuit of the oscillator tube. In this manner I provide an output current having a relatively true sine wave and characterized by a relatively constant frequency. Heretofore the plate or anode of the oscillator tube always aflorded the output current, and if a sine wave was desired, such output ourrent from the plate had to be passed through suitable expensive filters or other devices. It was a considered that the grid circuit could not be used to furnish the output energy of the tube, because the grid is the controlling element of the tube, and

hence could not be disturbed in any manner without materially aifecting the frequency. Finding that a true sine current exists in the grid circuit of the tube, I have devised the present invention whereby a relativelytrue sine wave is obtainable at relatively constant frequency and with only a 5 relatively insignificant change in frequency, so that filters and other controls could be avoided and the simplicity of the system maintained in a high degree, since it required merely a somewhat greater amplification than would be necessary 10 for a current derived from the plate circuit. These results I have accomplished by obtaining a radio tube that operates at audio frequency, utilizing a low impedance in the grid circuit thereof to thus diminish variations in frequency such as those caused by variations in line voltage, and then associating with the grid circuit a suitable condenser or inductance means of such small capacity as not to materially affect the frequency of the tube while obtaining the sine wave that occurs in said grid circuit. Because audio frequency is relatively low, any disturbance in fre quency that may be caused by said condenser or inductance means is correspondingly small, and

of course the low impedance condition cooper- 25 ates to further aid in maintaining the desired frequency.

The term audio frequency as used herein is intended to include the low ranges of radio frequency and also the inaudible frequencies below 30 audio frequency.

Referring in detail to the drawing, i 0 denotes a device embodying the invention. The same may be any conventional or suitable oscillator, in that the tube and circuit are generally speaking well 35 known, so that the drawing is not submitted in a limiting sense. For example, the oscillator may include a radio tube Ii having a filament I 2. a cathode iii, an anode or plate It, and a grid i5. all in suitable cooperative relation to each oth r. 40 Connected to the. grid I5 is any suitable gr d 0 cuit i6 comprising an inductance means. The grid circuit i6 preferably includes a low impedance inductance means comprising a low resistance inductance coil i! that is desirably free of 45 any iron core. Said cell may be connected at one end to the grid at i8 and may be grounded at its other end at l8. At a suitable intermediate point, a line 20 may connect the inductance coil to the cathode i3. Connected across the grid 50 circuit is a relatively high capacity condenser 2i hereinafter described.

Connected into the grid circuit as at l8 but preferably to inductance coil I 1 as at an adjacent or intermediate point as at 22 is an output line 55 23, having an output condenser 24 therein of relatively small capacity. The output line 23 may lead to any device 25 .that may be grounded at 26. The device 25 may be considered as being an amplifier or as including an amplifier, and may be also representative of a tuning or television system or any other means which may advantageously employ a sine wave at constant, audio frequency.

Associated with a suitable portion of the inductance coil ll an inductance coil 21 having a relatively small inductive capacity, and which is connected into a circuit 28 for a device 29 similar to the device 25. It will be understood that the condenser 24 and the inductance coil 27 are alternative arrangements and are shown herein to illustrate that either a condenser or an inductance coil-may be used for the grid circuit output. Generally speaking, both the condenser 24 and coil 21 may be referred to as a reactance means. The latter term'is also intended to include a resistor which may be used in place of the output condenser or inductance. The characteristics of the coil 21 may be sufflciently indicated to those skilled in the art by a consideration of the condenser 24, as hereinafter stated.

Since, according to the present invention, the plate I4 is not used as the output source, it is merely connected to a source of electrical potential 30 that is suitably grounded at 3 I. However, the plate circuit may be used as an output circuit simultaneously with the grid circuit, and such an arrangement may have advantages for certain purposes.

If the present invention be used in my patent application, Serial No. 151,349, filed July 1, 1937, for Electrical musical instruments, the grid output herein described is merely connected up in the same manner as the plate output was connected in the prior application above referred to. If desired, a single tube ll may be used, and diiferent circuits as herein shown, arranged for diiferent frequencies, may be interchangeably connected to the tube to produce different notes.

The capacity of the condenser 24 may be willciently small, in order not to materially disturb the conditions in the grid circuit, so that any change in frequency may be kept within about one-half of one percent. Within the range of audio frequency, this change is relatively negligible. The change will be less for lower, and greater for higher frequencies within the audio range, but for most practical purposes may be disregarded. By following the teaching of my invention, namely, keeping the impedance as low as possible, and using an output reactance means that is as small as possible, this change in frequency may be readily reduced to 0.001 percent or in fact to almost any value desired. If desired, the device I may, of course, be calibrated or standardized for the frequency of the grid cir-' cuit output. The capacity of the condenser 24 is preferably much smaller than that of the condenser 2l. The latter has suiilcient capacity, desirably just short of the peak point, at which the condenser capacity may cause the oscillations to cease. The condenser 2| may therefore be considered as having a large capacity. of course, if constancy of frequency in a high degree is not required, the capacity of the condenser 2| may be reduced, or the impedance of the grid circuit may otherwise be permitted to be higher than the low impedance hereinbefore referred to. Within the scope of the invention a small iron core may be used for the inductance coil ll. al-

though the absence of any iron core is the preferred condition.

It is noted that the connection for the output 23 is preferably taken somewhat remotely from the grid l5, as at 22, in order to minimize possible disturbance of the normal action of the grid.

It will now be perceived that the invention provides a novel device for directly obtaining constant audio frequency sine wave currents, without requiring the use of filters, by pass condensers, and the like, and that this is done by using a grid circuit having low impedance and utilizing the grid circuit as the output source and without materially affecting the normal action of the grid. Where the device is operated by current taken from a generator, the low impedance tends to avoid undue variations in frequency due to variations in line voltage. It will be observed that the invention may be used for various purposes as a new oscillator wherever its advantages are desired.

Because of the many variable factors involved herein, no specific details or formulas can be furnished, it being suiiicient that the condenser 2| can be increased in size to the point or points within the range hereinbefore described. It may be mentioned, however, that within the range of audio frequency, from zero to 1000 cycles, this invention permits the plate voltage to be doubled without requiring an unduly large inductance coil, and with the stability of this very simple system being maintained; and that a true sine wave can, if desired, be obtained as a result of the condenser 2i, by associating the output circuit with the inductance between the cathode and grid connections.

I claim:

1. An oscillator comprising a space discharge tube having an anode, a cathode and a grid, an inductance between said anode and grid, a connection to the cathode from an intermediate point of said inductance, a condenser connected across said inductance having such value as to be just short of preventing oscillation, means for grounding said anode for oscillation frequency, and means for taking oil output oscillation energy from said inductance between the connections to said grid and cathode, said oscillator being constructed and arranged to operate at audio frequency.

2. An oscillator of high degree of frequency stability comprising a space discharge tube having a cathode, an anode and a grid, an inductance connected between said anode and grid, an intermediate point of said inductance being connected to the cathode, a condenser connected in parallel with said inductance, said condenser having such capacity so large that it is Just short of that capacity which would preventoscillation, said oscillator being constructed and arranged to operate at audio frequency.

3. An oscillator of high degree of frequency stability comprising a space discharge tube having an anode, a cathode and a grid, an inductance between said anode and grid, a connection to the cathode from an intermediate point of said inductance, a condenser connected across said inductance having such value so large as to .be just short of preventing oscillation, and means for taking oil output oscillation energy from said inductance between the connections to said grid and cathode, said oscillator being constructed and arranged to operate at audio frequency.

4. An oscillator of high degree of frequency stability comprising a space discharge tube having a cathode, an anode and a grid, an inductance connected between said anode and grid, an intermediate point of said inductance being connected to the cathode, a condenser connected in parallel with a substantial portion of said inductance, said condenser having such capacity so large that is is just short of that capacity which would prevent oscillation and said oscillator being constructed and arranged to operate at audio frequency.

5. An oscillator of high degree of frequency stability comprising a space discharge tube hav-- ing a cathode, an anode and a grid, an inductance connected between said anode and grid, an intermediate point of said inductance being connected to the cathode, a condenser connected in parallel with a substantial portion of said inductance, said condenser having such capacity so large that it is just short of that capacity which would prevent oscillation, said anode being grounded for oscillation frequency, and said oscillator being constructed and arranged to operate at audio frequency.

6. An oscillator of high degree of frequency stability comprising a space discharge tube having an anode, a cathode and a grid, an inductance between said anode and grid, a connection to the cathode from an intermediate point of said inductance, a condenser connected across said inductance having such value so large as to be just short of preventing oscillation, means for grounding said anode for oscillation frequency, said oscillator being constructed and arranged to operate at audio frequency.

JEROME MARKowrrz. 

